Gene mutation possible link between autism and cancer

Originally published August 13, 2013 at 2:32 pm

Updated August 13, 2013 at 7:20 pm

Lucy Dabinett with her 9-year-old son, Tommy, who has autism caused by a PTEN gene mutation, at their home in Rye, N.Y. Researchers say mutated cancer or tumor genes in some people with autism caused their brain disorders.

Researchers studying two seemingly unrelated conditions — autism and cancer — have unexpectedly converged on a surprising discovery. Some people with autism have mutated cancer or tumor genes that apparently caused their brain disorder.

Ten percent of children with mutations in a gene called PTEN, which cause cancers of the breast, colon, thyroid and other organs, have autism. So do about half of children with gene mutations that can lead to some kinds of brain and kidney cancer and large tumors in several organs, including the brain. That is many times the rate of autism in the general population.

“It’s eerie,” Evan Eichler, a professor of genome science at the University of Washington, said about the convergence.

He and others caution that the findings apply to only a small proportion of people with autism; in most cases, the cause remains a mystery. And as with nearly all genetic disorders, not everyone with the mutations develops autism, cancer or other disorders associated with the genes, like epilepsy, enlarged brains and benign brain tumors.

But researchers say the findings are intriguing, given that there are no animals that naturally get autism, no way of analyzing what might cause autism in developing brains and no cure. The newly discovered link has enabled scientists to genetically engineer mice with many symptoms of the human disorder.

And it has led to the first clinical trial of a treatment for children with autism, using the drug that treats tumors that share the same genetic basis.

Richard Ewing of Nashville, Tenn., a 10-year-old who has a form of autism caused by a tumor-causing gene, is among those in the new study. His parents, Alexandra and Rick Ewing, know he is at risk for tumors in the brain, heart, kidney, skin and eyes. But that bad news was tempered by his eligibility for the clinical trial, which has only just started.

“There is a big difference between us and the rest of the autism community,” Rick Ewing said. “We have an honest-to-God genetic diagnosis.”

Not everyone agrees that the discovery is so promising. Steven McCarroll, a geneticist at Harvard, notes that autistic children with the cancer-gene mutation have “a brain that is failing in many ways.”

Autism in these children could be a manifestation of a general brain malfunction, he said, adding, “The fact that autism is one of the many neurological problems that arise in these patients doesn’t necessarily tell us anything penetrating about the social and language deficits that are specific to autism.”

But other scientists who are not involved in the research that produced these findings say the work is changing their understanding of autism and why it develops. Like cancer, autism can involve unregulated growth of cells, in this case neurons in the brain.

Jonathan Sebat, chief of the Beyster Center for Molecular Genomics of Neuropsychiatric Diseases at the University of California, San Diego, describes the parallels between cancer and autism as “quite uncanny.”

“We haven’t solved it all; we have only solved a tiny bit,” he said. “But the small bit we solved has been very illuminating.”

It was Dr. Charis Eng, a cancer geneticist at the Cleveland Clinic, who first noticed a surprising incidence of autism in children whose parents had the PTEN mutation (pronounced p-10). Eventually, investigators discovered that the rate of autism was 10 percent, about 10 times what would normally be expected.

At the same time, researchers found that another genetic disorder was even more likely to result in autism. That disorder, tuberous sclerosis, increases the risk for kidney cancer and a type of brain cancer; half of tuberous-sclerosis patients had autism.

Although PTEN and tuberous-sclerosis genes are not the same, they are part of the same network of genes that put a brake on cell growth. Disabling PTEN or one of the tuberous-sclerosis genes releases that brake. One result can be cancer or tumors. Another can be abnormal wiring of nerve fibers in the brain and autism.

Dr. Mustafa Sahin of Boston Children’s Hospital decided to test whether drugs used to treat tumors caused by tuberous-sclerosis gene mutations might also treat autism in people with the same mutated genes.

He started with mice, deleting tuberous-sclerosis genes in their cerebellums. Nerve fibers in the animals’ brains grew wildly, and the mice had unusual behaviors, reminiscent of autism. They had repetitive movements and groomed themselves constantly, so much that they sometimes rubbed their skin raw. And unlike normal mice, which prefer other mice to an inanimate object, these mice liked a plastic cup just as much.

But rapamycin, which targets the tuberous-sclerosis gene and blocks a protein involved in cell division, changed the animals. They no longer compulsively groomed themselves, and they no longer liked the plastic cup as much as a live mouse. The animals did better on tests of learning and memory, and the growth of nerve fibers in their brains was controlled.

Now Sahin is giving a similar drug, everolimus, to autistic children with a tuberous-sclerosis gene mutation, asking if it can improve their mental abilities. Richard is among the children. Each child takes the drug or a placebo for six months. The study is scheduled to be completed by December 2014.

While Eng started with cancer-gene mutations and discovered a link to autism, Eichler, of the UW, started with autism and found a connection to cancer genes.

He focused on what he calls “out of the blue autism,” which occurs with no family history, recruiting 209 families with autistic children.

He saw a striking genetic difference. Compared with their parents and normal siblings, the autistic children had two to three times as many mutations that disabled a gene. The mutated genes were often part of a pathway that controls cell growth. At first, the researchers thought the pathway was ubiquitous, and its link to autism was murky.

“We were a bit bummed,” Eichler said. “Then I said, ‘Wait, some of those genes are cancer genes.’ ”

But he does not yet know whether these children with autism are also at risk for cancer.